Astrophysics CubeSat Demonstrates Big Potential in a Small Package

The ASTERIA satellite, which was deployed into low-Earth
orbit in November, is only slightly larger than a box of cereal, but it could
be used to help astrophysicists study planets orbiting other stars.

Mission managers at NASA's Jet Propulsion Laboratory in
Pasadena, California, recently announced that ASTERIA has accomplished all of
its primary mission objectives, demonstrating that the miniaturized
technologies on board can operate in space as expected. This marks the success
of one of the world's first astrophysics CubeSat missions, and shows that small,
low-cost satellites could be used to assist in future studies of the universe
beyond the solar system.

"ASTERIA is small but mighty," said Mission Manager Matthew
W. Smith of JPL. "Packing the capabilities of a much larger spacecraft into a
small footprint was a challenge, but in the end we demonstrated cutting-edge
performance for a system this size."

Seeing
Stars

ASTERIA, or the Arcsecond Space Telescope Enabling Research
in Astrophysics, weighs only 22 pounds (10 kilograms). It carries a payload for
measuring the brightness of stars, which allows researchers to monitor nearby
stars for orbiting exoplanets that cause a brief drop in brightness as they
block the starlight.

This approach to finding and studying exoplanets is called the
transit method. NASA's Kepler Space Telescope has detected more than 2,300
confirmed planets using this method, more than any other planet-hunting
observatory. The agency's next
large-scale, space-based planet-hunting observatory, the Transiting Exoplanet
Survey Satellite (TESS), is anticipated to discover thousands of exoplanets and
scheduled to launch from Cape Canaveral Air Force Station in Florida on April
16.

In the future, small satellites like ASTERIA could serve as
a low-cost method to identify transiting exoplanets orbiting bright, Sun-like
stars. These small satellites could be used to look for planetary transits when
larger observatories are not available, and planets of interest could then be
studied in more detail by other telescopes. Small satellites like ASTERIA could
also be used to study certain star systems that are not within the field of
view of larger observatories, and most significantly, focus on star systems
that have planets with long orbits that require long observation campaigns.

The ASTERIA team has now demonstrated that the satellite's
payload can point directly and steadily at a bright source for an extended
period of time, a key requirement for performing the precision photometry
necessary to study exoplanets via the transit method.

Holding steady on a faraway star is difficult because there
are many things that subtly push and pull on the satellite, such as Earth's atmosphere
and magnetic field. ASTERIA's payload achieved a pointing stability of 0.5
arcseconds RMS, which refers to the degree to which the payload wobbles away
from its intended target over a 20-minute observation period. The pointing
stability was repeated over multiple orbits, with the stars positioned on the
same pixels on each orbit.

"That's like being able to hit a quarter with a laser
pointer from about a mile away," said Christopher Pong, the attitude and
pointing control engineer for ASTERIA at JPL. "The laser beam has to stay
inside the edge of the quarter, and then the satellite has to be able to hit
that exact same quarter -- or star -- over multiple orbits around the Earth. So
what we've accomplished is both stability and repeatability."

The payload also employed a control system to reduce
"noise" in the data created by temperature fluctuations in the satellite,
another major hurdle for an instrument attempting to carefully monitor stellar
brightness. During observations, the temperature of the controlled section of
the detector fluctuates by less than 0.02 Fahrenheit (0.01 Kelvin, or 0.01
degree Celsius).

Small
satellites

ASTERIA is a CubeSat, a type of small satellite consisting
of "units" that are 10 centimeters cubed, or about 4 inches on each side.
ASTERIA is the size of six CubeSat units, making it roughly 10 centimeters by
20 centimeters by 30 centimeters. With its two solar panels unfolded, the
satellite is about as long as a skateboard.

The ASTERIA mission utilized commercially available CubeSat
hardware where possible, and is contributing to a general knowledge of how
those components operate in space.

"We're continuing to
characterize CubeSat components that other missions are using or want to use,"
said Amanda Donner, mission assurance manager for ASTERIA at JPL.

ASTERIA launched to the International Space Station in
August 2017. Having been in space for more than 140 days, the satellite is operating
on an extended mission through May.

ASTERIA was developed under the Phaeton Program at JPL.
Phaeton provides early-career hires, under the guidance of experienced mentors,
with the challenges of a flight project. ASTERIA is a collaboration with the
Massachusetts Institute of Technology in Cambridge; where Sara Seager is the
principal investigator.